This study will define how specific features of movements are represented in the motor output of the central nervous system in man. At present, there is only a rudimentary understanding of how the human brain controls limb movements, particularly of the thumb and digits. The specific aims of the proposed study are to define what movement and digits. The specific aims of the proposed study are to define what movement variables are controlled by the central nervous system during the performance of voluntary ballistic movements of the thumb and index finger. This study will evaluate scalp-recorded cerebral potentials associated with a specific movement, under controlled movement conditions in which one variables are force, displacement and movement time. The proposed studies will examine the role of force opposing movement, acceleration and index finger and both digits operating together in a pinch movement. The question of how motor control is modified to accommodate an unexpected load will be evaluated in order to determine which components of cerebral movement-related potentials reflect specific features of the unexpected load. Repetitive movements of the thumb well be studied in order to define the characteristics and timing of cerebral potentials associated with each phase of successive flexion- extension movements and how an unexpected load will alter such relationships. Experiments will evaluate different movement strategies when subjects use movement time, velocity or force as their primary control strategies in movement performance. The long term objectives of the proposed study are to understand the motor control of the human thumb and digits, since the ability to perform fine dexterous movements with the hand is one of the most important tasks used in daily life. As the characteristics of motor control of the digits becomes better understood, new diagnostic evaluations studying cerebral movements related potentials in patients following hemispheric stroke will be possible with the potential for better prognostic evaluations. The characterization of movement related potentials will have important implications for the design of control signals used for neuroprosthetic devices in paralyzed or otherwise handicapped individuals.